P1. Syst. Evol. 165, 159-188 (1989) Plant Systematics and Evolution © by Springer-Verlag1989 Patterns of genetic variation of the genus Capsicum (Solanaceae) in Mexico FERNANDOLOAIZA-FIGUEROA, KERMIT RITLAND, JOSEA. LABORDECANCINO, and S. D. TANKSLEY Received July 15, 1987 Key words: Angiosperms, Solanaceae, Capsicum.- Isozymes, genetic distance, geographic differentiation. Abstract: The evolutionary relationships of 186 accessions of Capsicum from Mexico were studied through enzyme electrophoresis. A total of 76 alleles representing 20 genetic loci coding for nine enzyme systems were observed and the allelic variations of enzymes were studied for geographical distribution. Allele frequencies were used to estimate the appor- tionment of gene diversity within and between populations and to construct a dendrogram based on a similarity matrix containing NEI genetic distances. - The gene diversity estimates suggest that the structure of Capsicum populations in Mexico consists of predominantly homozygous genotypes presumably due to a self-pollinated breeding system and population bottlenecks. Significant genetic differentiation was found mainly between populations of differing geographical regions.- Based on the results of this study, three species of do- mesticated Capsicum can be identified in Mexico, C. annuum var. annuum, C. chinense, and C. pubescens. Semidomesticated and wild forms include two species, C. frutescens and C. annuum vat. glabriusculum. A sharp geographical division results between the latter species; C. frutescens was collected exclusively in the southeastern states of Oaxaca, Chiapas, and Tabasco; whereas wild and semidomesticated forms from the rest of the country are C. annuum. Based upon the similarity of enzyme genotypes of semidomesticated and wild forms, the primary center of domestication of cultivated C. annuum was estimated to be the region comprising the states of Tamaulipas, Nuevo Leon, San Luis Potosi, Veracruz, and Hidalgo in eastern Mexico. A possible second center of domestication is suggested to be localized in the state of Nayarit, western Mexico. Capsicum (Solanaceae) is a New World genus with approximately 27 species. Of these, C. annuum, C. frutescens, C. chinense, C. baccatum, and C. pubescens are domesticated (Genetic Resources of Capsicum 1983). This genus has its center of origin in South America, where 22 of the species are endemic (HUNZIKEP, 1979). The basic chromosome number of all the Capsicum species is x = 12 except for C. ciliatum (H. B. K.) O.K. and an undetermined species from Brazil whose basic chromosome number are x = 13, and a tetraploid domesticated C. annuum accesion (PIcKERSGILL 1977). The generic limits of Capsicum include all the forms with free,